Disappearing plug

ABSTRACT

In an embodiment of the present invention utilizes a frac plug having a large diameter through bore wherein the through bore is at least 75% of the outer diameter of the plug. A tracer assembly is then affixed to a lower end of frac plug. The frac plug tracer assembly is run into a wellbore where the frac plug is then set, perforated, and fracked. The obstruction within the frac plug through bore is then removed. In some instances, the instruction may be a ball, dart, or other obturator and in some instances the obstruction may be a dissolvable plug. With the obstruction within the frac plug through bore removed wellbore fluids from the hydrocarbon formation may flow upward through and around the tracer assembly picking up chemical traces which are then carried to the surface to be analyzed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 62/512,630 that was filed on May 30, 2017.

BACKGROUND

One method of completing a well is known as plug and perf. The plug and perf operation typically begins after the well has been drilled and cased. Once the operator is ready to begin the plug and perf operation a perforating tool is assembled on the surface. The perforating tool typically incorporates a plug on the lower end. The plug, once moved into position and set, will lock into the casing walls and form a fluid tight seal preventing fluid from moving past the plug. Just above the plug is a setting tool. The setting tool, once actuated, moves the plug from an unset position where the plug can be run into the well to a set position where, as previously mentioned, the plug locks into the casing and blocks fluid flow. Just above the setting tool is the perforating gun. The perforating gun usually but not always consists of one or more shaped charges that, upon detonation, will form holes in the casing wall. Any type of perforating tool may be used such as a jetting tool, etc.

Once assembled on the surface the perforating tool is run into the well to the desired depth. Once the desired depth is reached the setting tool is actuated to move the plug from its unset position to its set position locking the plug in place. The setting tool then disconnects from the plug. After disconnection the setting tool and the perforating gun are raised to some point above the now set plug, preferably to a location adjacent to a hydrocarbon formation. Once the perforating gun is in place the perforating gun is actuated thereby forming holes or perforations through the casing wall. The perforating gun and setting tool are then usually but not always removed from the wellbore.

With the perforating gun and setting tools removed from the wellbore the well may be fractured through the perforations formed by the perforating gun. Fracturing usually occurs by pumping high-pressure fluid through the casing to the plug once the fluid reaches the plug it can no longer flow downward as the plug forms a fluid tight seal and is locked to the. High-pressure fluid then flows laterally outward through the holes in the casing. The fluid cracks and/or removes the cement adjacent to the perforations continuing to move outward into the rock formations fracturing the rock and allowing hydrocarbons to flow in towards the casing, once the fracking ceases.

Once the well has been fraced at the first location a second perforating tool may be assembled on the surface and then run into the wellbore to a second location above the location of the first perforations. The procedure is then repeated until all known formations have been accessed through the casing by perforations. After the plug and pert operations are completed the plugs are removed from the well. In some instances, the plugs may dissolve in other instances the plugs may be drilled. In other instances, the plugs have large internal bores with a seat within the plug allowing a ball, dart, or other obturator to form a seal with the seat to block downward flow. By having an obturator, during reverse flow, such as when hydrocarbons are being produced to the surface, the ball will lift off of the plug seat allowing fluid to flow upwards through the plug. In other instances, the plugs may have a dissolvable core such that after the perforating operation the internal bore of the plug will dissolve allowing production through the center of the plug while the plug and any items attached to the plug remain in place within the wellbore.

Once the plugs are removed hydrocarbons from each of the various formations flow into the interior of the casing and following the path of least resistance to the surface. One of the downsides of allowing the hydrocarbons from the various formations to co-mingle within the interior of the casing is that it is difficult to tell whether or not fluid is being produced from a particular formation and what is the makeup of the fluid being produced from a particular formation, i.e. has the formation watered out or is it still producing hydrocarbons. Presently determining the production characteristics of a well requires running expensive logging operations into the well after the plug and perf job is completed.

SUMMARY

It has been found that by adding a chemical or other tracer at various locations along the wellbore, once the fluid reaches the surface the fluid may be analyzed with the various markers i.e. tracers and formation production parameters may be assessed.

It is the objective of some operators to understand the effectiveness of the plug and pert frac job by understanding which portions of the reservoir are contributing the maximum production. In the present embodiment the operator would use a big bore frac plug as the bottom portion of the perforating tool. The big bore frac plug has, as the name implies, a large internal diameter and seals against downward fluid flow with a ball, dart, or other obturating device on a seat within the big bore frac plug. Preferably the ball, dart, plug core, or other obturator is dissolvable. In some instances, dissolution of the ball takes place in the presence of hydrocarbons or water and in other instances a chemical agent is supplied to either accelerate or cause dissolution of the obturator. The chemical dissolution agent may be supplied with the frac fluid or as a delayed release component of the obturator or frac plug.

In a present embodiment the big bore frac plug is modified to allow chemical tracers to be attached to the big bore frac plug either directly or within a chemical tracer carrier. In some instances, the chemical tracers are attached to the lower portion of the big bore frac plug, in other instances the chemical tracers are attached above the big bore frac plug, and in still other instances the chemical tracers are carried within the big bore frac plug. It is envisioned that the big bore frac plug is adapted so that a tracer carrier having the same internal diameter as the big bore frac plug is fitted to receive chemical tracers and is able to be easily attached to the big bore frac plug such as by threading, shear pins, etc. Additionally, the tracer carrier allows the wellbore fluid to interact with the chemical tracers such that the wellbore fluid will carry a portion of the chemical tracer with the fluid to the surface.

Once the big bore frac plug is run into the hole and set, using either a wire line or coil tubing setting tool, the running assembly is then disconnected from the plug and the perforations are created above the plug by locating and firing the perforating guns. The spent guns and setting tool are then removed from the well. After removal, an obturator such as a dissolvable frac ball is dropped to land on the frac plug creating the isolation between an upper (newly perforated) zone and a lower (recently stimulated) zone. A further function of the ball is to isolate the frac job to be performed on the upper zone from the tracer carrier located below the frac plug.

Once all zones have been fractured, the operator may perform well cleanup or flowback operations to bring the well onto production. The dissolvable frac balls or plug core begin dissolving and disappear in a designated period of time. The big bore frac plug's relatively large internal diameter as compared to its outer diameter, usually over 75%, provide minimum restriction through the internal diameter allowing the well to flow. Once the well is cleaned up, the well may be shut in for a designated interval. The shut-in interval allows the chemical tracer carriers to release the initial chemical tracer loads into the fluid the chemical tracer is exposed to. Following the pre-planned period of chemical build up time, the well is then turned back on to flow and a chemical sample is captured at the surface allowing the operator to develop a profile of the flow contribution (media type and production levels) from the various well sections to understand the effectiveness of the frac job in the well completion plan. Knowing the well flow characteristics helps the operator in designing future wells for optimize performance in the same reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a wellbore after the casing has been run into the wellbore and plugs with tracers have been installed.

FIG. 2 is a close-up side view of a wellbore and a tracer assembly.

DETAILED DESCRIPTION

The description that follows includes exemplary apparatus, methods, techniques, or instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details.

FIG. 1 depicts a wellbore 10 after the casing 30 has been run into the wellbore 10. The casing has a toe plug 26 at the lower end 32 of the wellbore 10. The wellbore 10 has been fractured creating a first zone 40 and a first producing zone 12. A first plug 20 including a tracer assembly 21 has been set in place above first producing zone 12. A first ball 42 has been landed atop first plug 20 allowing the casing 30 to be perforated adjacent a second producing zone 14 creating a second zone 43. A second plug 22 including a tracer assembly 23 has been set in place above second zone 43. A second ball 44 has been landed atop second plug 22 allowing the casing 30 to be perforated adjacent a third producing zone 16 creating a third zone 46. A third plug 24 including a tracer assembly 25 has been set in place above third zone 46. A third ball 48 has been landed atop third plug 24 allowing the casing 30 to be perforated adjacent a fourth producing zone 18 creating a fourth zone 50. With all zones perforated the operator may shut-in the well for a predetermined period of time to allow fluids adjacent to each tracer assembly 21, 23, and 25 to become appropriately loaded with the various tracers. The tracers may be chemical, biological, radioactive, electronic, or mechanical. In some instances, the tracer assemblies may carry chemicals such as paraffin inhibitors, biocides, corrosion inhibitors, or other chemicals useful in a wellbore.

FIG. 2 is a close-up side view of wellbore 10 at tracer assembly 23. In this instance second plug 22 is shown in its set position gripping casing 30. In this instance while the dissolvable frac ball 44 is shown in its seated position the well is being produced so that fluids flowing from producing zone 14 into second zone 43 are then flowing towards third zone 46 through and around tracer assembly 23. Arrow 76 depicts the flow path of fluids flowing from producing zone 14 into second zone 43. As the fluids approach tracer assembly 23 which is locked into position within the casing 30 by the large internal diameter frac plug 22. As indicated by arrow 78 some of the fluid may flow through the center of the tracer assembly 23 while some of the fluid flows into an annular chamber 80 created by the casing 30 and the outer diameter of the tracer assembly 23. The fluid flow path into annular chamber 80 and then through various ports 70 along the length of the tracer assembly 23 as indicated by arrow 74. As the fluid flows through various ports 70 and around tracer assembly 23 the fluid picks up small portions of the tracer in tracer assembly 23. The fluid then carries the tracer to the surface where the operator is able to utilize the tracer from each of the tracer assemblies 21, 23, and 25 to determine the composition of the fluid produced at a particular location as well as the volume of fluid produced from each producing zone.

The methods and materials described as being used in a particular embodiment may be used in any other embodiment. While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible.

Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter. 

What is claimed is:
 1. A device for placing chemicals within a wellbore comprising, a plug having a through bore and a slip about its exterior circumference for gripping the wellbore, a tracer assembly including a tracer, wherein the tracer assembly is attached to the plug, wherein an annular chamber is formed between the exterior circumference of the tracer assembly and the interior circumference of the wellbore, ports formed through the tracer assembly allowing a fluid to flow between the annular chamber and an interior of the tracer assembly.
 2. The device of claim 1 wherein, the through bore's internal diameter is at least 75% of the plug's outer diameter.
 3. The device of claim 1 further comprising, a ball to seal on the through bore.
 4. The device of claim 1 further comprising, a dissolvable plug within the through bore.
 5. The device of claim 1 wherein, the tracer assembly includes at least two tracers.
 6. The device of claim 1 wherein, the tracer is radioactive.
 7. The device of claim 1 wherein, the tracer is chemical.
 8. A method of placing a tracer the wellbore comprising, assembling a plug and tracer assembly, placing the plug having a through bore and tracer assembly within a wellbore, sealing the plug and fracking a producing zone, removing the plug, entraining a tracer from the tracer assembly into a produced fluid.
 9. The method of claim 8 wherein, the through bore's internal diameter is at least 75% of the plug's outer diameter.
 10. The device of claim 8 further comprising, a ball to seal on the through bore.
 11. The device of claim 8 further comprising, a dissolvable plug within the through bore.
 12. The device of claim 8 wherein, the tracer assembly includes at least two tracers.
 13. The device of claim 8 wherein, the tracer is radioactive.
 14. The device of claim 8 wherein, the tracer is chemical. 